The present invention relates to an image forming apparatus having a function to feed a specific sheet each time a predetermined number of images are formed.
An image forming apparatus has been proposed heretofore which apparatus is capable of operating at a mode (hereinafter called a cover mode) where a specific sheet with or without an image copied thereon is inserted as the cover for a certain number of originals or for a unit number of originals. This mode is a mode during which a different color sheet is inserted as a cover, or a separation sheet is inserted for an optional number of originals.
Also known is an automatic document feeder for an image forming apparatus which is capable of operating at a mode (hereinafter called an APS mode) where an original size is detected through preliminary scan of an original, and a cassette of a suitable sheet size is automatically selected based on the detected original size information and a copy magnification factor.
When the cover mode and the APS mode are both employed in the apparatus operation, if the cassette selected as suitable size during the APS mode is the specific cassette for the cover mode, then a sheet feed is carried out from the cover mode specific cassette contrary to the intention of an operator. Also, in the operation using both the cover mode and the APS mode, if the sheet size of the cassette selected as suitable during the APS mode differs from the size of a cover sheet in the specific cassette, then there occurs the problem that the finished set of the cover and copied originals has different sizes for the cover and the copied originals.
There is also known an image forming apparatus capable of operating at a mode (hereinafter called an ACC mode) where if all transfer sheets within the presently selected cassette have been consumed during the copy operation, a cassette having sheets of the same size is checked, and if present, the sheet feed cassette is automatically changed to that cassette.
If both the cover mode and the ACC mode are employed and when all transfer sheets within the cassette have been consumed, automatic cassette change function is actuated to select a cassette of the same sheet size, if any, to thereby continue the copy operation. However, if the selected cassette is the specific cassette for the cover mode, there occurs the problem that the operation not intended by the operator will be carried out.
Also generally known is a copying apparatus capable of copying a one side original onto the both sides of a recording member or sheet. If the both sides copy operation is carried out using one side originals including a cover original and if the number of originals is even, then the back side of the cover is also copied.
An apparatus has also been proposed which is provided with a plurality of color developing units and can form images by selecting a color used during the operation of forming a set of images. However, color cannot be changed on the way of forming a set of images.
Therefore, even if the cover mode function is provided for such an image forming apparatus, the cover is copied with the same color as the other originals. If the cover is to be copied with a different color, then an additional copy operation for that purpose only must be conducted, causing inconvenience for an operator.
Also known is an apparatus composed of a copying apparatus and a recycle type original document feeder (hereinafter called an RDF) which feeds documents placed on a tray one by one to the exposure site and after the exposure, returns a document to the same tray.
In performing a copy operation during the cover mode by using such an apparatus with RDF, even if a sheet different from an ordinary recording sheet is intended to be used as the cover corresponding to the first page original, this first page original cannot be discriminated as to the timing when it comes. Therefore, whether a recording sheet or a cover sheet is fed cannot be determined until the sheet feeding of the originals excluding the cover original has been completed. Such arrangement increases the time required for the sheet feeding, resulting in a large time for forming a set of copies and in lowering the production efficiency.